Silica spheres are used in an extremely wide range of applications, including from industrial uses such as in various additives or catalysts to products for everyday use. Furthermore, such silica spheres are being investigated from various aspects, for possible introduction of functional molecules or organic materials, or the like, in accordance with the characteristics that are required by various applications.
With regard to the application of complex spheres in which functional molecules or an organic material is introduced to silica spheres, selection of the functional molecule or organic material to be introduced, the amount introduced, and the monodispersity of the spheres are considered as very important factors. As the monodisperse silica spheres having functional molecules or an organic material introduced, for example, spheres in which silica spheres that are surface-treated with a silane coupling agent are combined with functional molecules, are disclosed (see, for example, Patent Document 1). However, the spheres obtained from Patent Document 1 have functional groups on the sphere surfaces, but the structural body itself of the spheres is composed of silica only, thus the spheres are not spheres to which an organic material is introduced.
Also, as the spheres having an organic material introduced, for example, spheres in which an organic compound having a plurality of amino groups has been incorporated into silica spheres have been proposed (see, for example, Patent Document 2). However, since the spheres obtained from the Patent Document 2 include only an organic compound having amino groups, and silica, it is difficult to incorporate other functional molecules into the spheres. Furthermore, the process for producing the spheres is complicated as will be described later, it is difficult to control the sphere diameter, and the spheres do not show sufficient monodispersity.
In addition, spherical bodies obtained by synthesizing a self-emulsifiable compound by introducing a nonionic chain to a fluorescent molecule residue, and introducing silica to the compound, have been proposed (see, for example, Non-Patent Document 1). However, the spherical bodies disclosed in Non-Patent Document 1 have silica present only on the surface. Also, since complexation including silica is formed by using an O/W type emulsion, the production process is complicated, and it is difficult to achieve control of the particle diameter or homogenization, resulting in deteriorated monodispersity. Furthermore, since the spherical bodies (spheres) are based on emulsion particles, it is not possible to take the spheres out and process them into a powder.
On the other hand, for the application of complex spheres, it is important that how spheres with good monodispersity is produced. A significant number of the conventional silica spheres, and particularly monodisperse silica spheres, are produced by Stober's method in which an alkoxy silane is reacted in a mixture of an alcohol, highly concentrated ammonia and water to obtain spherical spheres (see, for example, Patent Document 2). Also for the method for obtaining silica spheres having functional molecules or organic materials introduced, improved versions of this Stober's method are being used. For example, a method of synthesizing a compound in which functional molecule residues are bonded to an alkoxy silane derivative, mixing this compound with a tetraalkoxy silane, and reacting the mixture in the same manner as in Stober's method; a method of synthesizing silica spheres by Stober's method, treating the sphere surface with a silane coupling agent, and further reacting the coupling agent with functional molecules (see Non-Patent Document 3); a method of introducing highly branched polyethyleneimine into silica by adding a small amount of highly branched polyethyleneimine to the highly concentrated ammonia medium in the Stober's method (see Patent Document 2), and the like are disclosed. However, in these improved versions of Stober's method, it is possible to incorporate functional molecules into the silica spheres, but the production processes are complicated, occasionally with low productivities. Furthermore, not all of these methods involve simultaneous introduction of functional molecules and organic materials. Moreover, these methods take long reaction times, or are associated with high environmental stress, such as a reaction condition of a high ammonia concentration being required, or the like.
In recent years, research on the synthesis of silica originating from biosilica has been conducted, and examination has been carried out on the synthesis of spherical silica in aqueous media under mild conditions using polyamines as templates. For example, examination has been carried out on synthesizing spherical silica in aqueous media using polypeptides or polypropyleneimines that are extracted from biosilica from a biological system, synthetic polyarylamine, block copolymers of polyamino acids, or the like (see, for example, Non-Patent Documents 4 to 6). However, in these methods, it is difficult to obtain uniformed spherical particles, and networks of bonded spheres are prevalently generated. Even in the case of obtaining individual spheres, they are obtained as mixtures of spheres of inhomogeneous size having no discrete particle diameters.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 6-100313    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2-263707    Non-Patent Document 1: R. H. Jin, Chem. Commun. (2002), p. 198; R. H. Jin, J. Mater. Chem., Vol. 14, p. 320 (2004)    Non-Patent Document 2: W. Stober et al., J. Colloid & Interface Sci., vol. 26, p. 62 (1968)    Non-Patent Document 3: A. Blaaderen et al., Langmuir, Vol. 8, p. 2921 (1992)    Non-Patent Document 4: N. Kroger et al., Proc. Natl. Acad. Sci. USA, Vol. 97, p. 14133 (2000)    Non-Patent Document 5: M. Sumper, Angew. Chem. Int. Ed., Vol. 42, p. 5192 (2003)    Non-Patent Document 6: Morse et al., Nature, Vol. 403, p. 289-292 (2000)